1. Field of the Invention
The present invention relates to a linear guide apparatus for supporting a movable member to be linearly movable on a guide member.
2. Description of the Related Art
A linear guide apparatus is used for moving, e.g., an optical or magnetic head of an optical disk drive or a hard disk drive (HDD) in the radial direction (i.e., tracking direction) of an optical or hard disk.
Usually, in a linear guide apparatus (to be merely referred to as a "guide mechanism" hereinafter), a movable member is provided with bearings. These bearings are brought into contact with parallel linear guide members fixed to a stationary chassis of an equipment that uses the linear guide mechanism, thereby guiding the movement of the movable member along the extending direction of the guide members. A small gap is formed between each of the bearings and the corresponding guide member to accept the manufacturing allowances of the bearings and the guide members and to guarantee smooth movement of the bearings on the guide members. These gaps cause rattle, although very small, in the bearings when the bearings move along the guide members.
A linear guide apparatus having a mechanism for eliminating rattle is known in, e.g., Jpn. Pat. Appln. KOKAI Publication No. 4-243069. This conventional linear guide apparatus is used in an optical disk drive. As shown in FIGS. 1 and 2, a pair of first and second linear guide members 42a and 42b are provided on the upper surface of a stationary chassis 40 of the optical disk drive. The first and second guide members 42a and 42b extend parallel to each other in the radial directions (tracking directions), indicated by arrows X1 and X2, of an optical disk (not shown). A movable member 44 having an optical head 44a is arranged between the first and second guide members 42a and 42b above the upper surface of the stationary chassis 40. A pair of roller bearings 46 are rotatably mounted at two positions separated from each other by a predetermined distance in the tracking direction, on a side surface of the movable member 44 facing toward a direction indicated by an arrow Y1. One roller bearing 48 is rotatably mounted on a side surface of the movable member 44 facing toward a direction indicated by an arrow Y2. The roller bearing 48 is located between the pair of roller bearings 46 in the tracking directions indicated by the arrows X1 and X2.
The first guide member 42a on a side indicated by the arrow Y1 is fixed to a first positioning projection 40a on the upper surface of the stationary chassis 40, and the second guide member 42b on a side indicated by the arrow Y2 is mounted on the upper surface of the stationary chassis 40 through a position adjusting mechanism 50. The position adjusting mechanism 50 holds the second guide member 42b to be movable in the directions indicated by the arrows Y1 and Y2 in parallel to the first guide member 42a.
The position adjusting mechanism 50 has a pressing block 52 which is formed such that its section in a Y-Z plane forms a parallelogram so that it is movable on the upper surface of the stationary chassis 40.
As best shown in FIG. 1, first and second inclined side surfaces 52a and 52b of the pressing block 52 arranged in the directions indicated by the arrows Y1 and Y2 are inclined toward the second guide member 42b. The first inclined side surface 52a arranged in the direction indicated by the arrow Y1 contacts the first guide member 42a. A lower edge 52c, arranged in a direction indicated by an arrow Z1, of the second inclined side surface 52b arranged in a direction indicated by the arrow Y2 contacts a second positioning projection 40b extending on the upper surface of the stationary chassis 40 in the same manner as the second guide member 42b. The pressing block 52 is pivotal indicated by a double-headed arrow A with the lower edge 52c of the second inclined side surface 52b being functioning as a rotational center in directions.
A through hole 52d extending in the vertical direction (focusing directions) indicated by arrows Z1 and Z2 is formed in the pressing block 52, and a through hole is formed in the stationary chassis 40 to be concentric with the through hole 52d of the pressing black 52. A screw 54 with a head is inserted in the through hole 52d of the pressing block 52 and the through hole of the stationary chassis 40 from the pressing block 52 side. A nut plate 56 is threadably engaged with the distal end portion of the screw 54 at a position separated downward from the stationary chassis 40 in the direction indicated by the arrow Z2. The nut plate 56 is vertically movable on the lower surface of the stationary chassis 40 while its rotation is prohibited. A compression coil spring 58 is mounted on the screw 54 between the lower surface of the stationary chassis 40 and the nut plate 56.
In this arrangement, when the screw 54 is rotated in one direction to move the nut plate 56 close to the lower surface of the stationary chassis 40, the pressing block 52 is pivoted counterclockwise against the biasing force of the compression coil spring 58 with the lower edge 52c of the second inclined side surface 52b being functioning as the rotational center. As a result, the pressing block 52 presses the second guide member 42b by the first inclined side surface 52a to move the second guide member 42b toward the first guide member 42a. Then, the gaps between the first guide member 42a and the pair of roller bearings 46 of the movable member 44 and between the second guide member 42b and the roller bearing 48 are eliminated so that movement of the movable member 44 without rattle with respect to the first and second guide members 42a and 42b is guaranteed in this manner.
In the conventional apparatus shown in FIGS. 1 and 2, the degree of parallel between the first positioning projection 40a for the first guide member 42a on the upper surface of the stationary chassis 40 and the second guide member 42b for the second guide member 42b and for the passing block 52, and the degree of parallel between the extending direction of the lower edge 52c of the second inclined side surface 52b of the pressing block 52 abutting against the second positioning projection 40b and the first inclined side surface 52a of the pressing block 52 abutting against the second guide member 42b must be considerably high.
In order to satisfy this requirement, high-precision machining is required in the manufacture of the conventional apparatus shown in FIGS. 1 and 2. This increases the manufacturing cost of the conventional apparatus and leads to an increase in cost of the conventional apparatus.
Another linear guide apparatus having a mechanism for eliminating rattle is known in Jpn. Pat. Appln. KOKAI Publication No. 61-224171.
This another linear guide apparatus will be described with reference to FIGS. 3 to 5.
A pair of first and second linear guide members 62a and 62b extending parallel to each other in directions indicated by arrows X1 and X2 are provided on the upper surface of a stationary chassis 60. A movable member 64 is arranged between the first and second guide members 62a and 62b above the upper surface of the stationary chassis 60. A pair of roller bearings 66 are rotatably mounted at two positions separated from each other by a predetermined distance in the directions indicated by the arrows X1 and X2, on a side surface of the movable member 64 facing toward a direction indicated by an arrow Y1. One roller bearing 68 is rotatably mounted on a side surface of the movable member 64 facing toward a direction indicated by an arrow Y2. The roller bearing 68 is located between the pair of roller bearings 66 in the tracking directions indicated by the arrows X1 and X2.
The first guide member 62a arranged on a side indicated by the arrow Y1 is fixed on the upper surface of the stationary chassis 60. The two end portions, arranged in the directions indicated by the arrows X1 and X2, of the second guide member 62b arranged on a side indicated by the arrow Y2 are mounted on the upper surface of the stationary chassis 60 through a pair of position adjusting mechanisms 70. The pair of position adjusting mechanisms 70 hold the second guide member 62b to be movable in the directions indicated by the arrows Y1 and Y2 with the second guide member 62b being in parallel to the first guide member 62a, and have compression coil springs 70a for biasing the second guide member 62b toward the first guide member 62a.
In this another conventional linear guide apparatus, the second guide member 62b pressed against the roller bearing 68 of the movable member 64 between the pair of position adjusting mechanisms 70, is flexed at a portion abutted against the bearing 68 in the direction indicated by the arrow Y2. When the movable member 64 is moved along the first and second guide members 62a and 62b, the pressure applied to the compression coil springs 70a of the pair of positioning mechanisms 70 through the second guide member 62b change to expand or contract the compression coil springs 70a. Expansion/contraction of the compression coil springs 70a causes frictional resistance with respect to the housings accommodating the compression coil springs 70a to interfere with smooth expansion/contraction (i.e., smooth movement of the second guide member 62b) of the compression coil springs 70a. Then, frictional resistance generated between the movable member 64 and the first and second guide members 62a and 62b during movement of the movable member 64 is slightly changed, and leads to non-uniformity in moving speed of the movable member 64.